Update part-4.md
Update part-4.md

Corrected the api.event route. The "routes" was missing
app.post('/api/event', routes.api.event.post);

frontyard/keystone,frontyard/keystone,vokal/keystone,vokal/keystone,vokal/keystone,trentmillar/keystone,matthewstyers/keystone,trentmillar/keystone,matthewstyers/keystone,frontyard/keystone,trentmillar/keystone,Pop-Code/keystone,matthewstyers/keystone,Pop-Code/keystone